Very helpful discussion! Thanks to everyone for their input. I raised my seat to the highest it could go, which is also about the highest I can do to pedal naturally, without fully extending the leg at the lowest of the pedaling cycle. It makes great difference: feel much more comfortable in pedaling, much less knee stress when going uphill. I can't reach the ground with my toe while seated, even leaning slightly, but I'm not going to lower the seat back (until new problems occur), because then my lap would be near horizontal again at the top of pedaling.

(Btw, yes, I often avoid getting off the bike at red light by timing it so the light becomes green when I rolled to the intersection, behind or next to a stopped car.)